A prior starting device for a refrigerator compressor motor is explained with reference to FIG. 13. A single phase induction motor 20.comprising a main winding 22 and a starting winding 23 that is located in phase difference relationship with respect to main winding 22, is connected to a starting device comprising a positive temperature coefficient thermistor (hereafter referred to as PTC) in series with starting winding 23, and is connected to a source E via an overload relay 24. When voltage from source E is applied to single phase induction motor 20, since starting PTC 25 has a low resistance, large current flows through starting winding 23, then a rotator (not shown) is rotated. After single phase motor 20 has started, starting PTC 25 becomes a high resistance by self-heating of the current therein, therefore the current through starting winding 23 is significantly reduced, thus motor 20 becomes static.
However, in the above mentioned configuration, while starting, a large current of up to 10 amperes has to flow through the starting PTC during 0.5 to several seconds, which requires considerable heat capacity. Thus, even when the motor becomes static, the starting PTC consumes power of 2 W to 4 W in order to maintain the high temperature and resistance so as to reduce the current, which prevents energy-saving in the motor.
Furthermore, in the above mentioned configuration, while starting, there is a problem in that it is hard to restart the motor immediately after it has stopped. That is, since the starting PTC has a large heat capacity, once it reaches a high temperature and high resistance during operation, it takes approximately 20 to 30 seconds to several minutes after the motor is stopped to reduce to a near normal temperature, i.e., to return to a condition from which it can be restarted. Therefore, if one tries to start the motor before it reaches a suitable starting condition, only a small amount of current flows through the starting winding since the starting PTC is at high resistance, the rotator of the motor is locked, a large amount of current flows through main winding 22 to operate overload relay 24, and the motor is notable to be restarted. At the beginning, reset time of this overload relay 24 is shorter than the cooling time in which the starting PTC returns to suitable starting condition, overload relay 24 repeats the operation and reset several times and the temperature thereof rises to increase the reset time. When the reset time of overload relay 24 becomes longer than the above mentioned cooling time of the starting PTC, the motor can be restarted. That situation happens, for example, when a door thereof is opened and the temperature in the refrigerator rises to turn on the thermostat, immediately after which the refrigerator compressor motor is stopped by turning off the thermostat on account of a drop in temperature in the refrigerator. In such case, not only does it take time to restart the motor, but also the life of the overload relay is shortened by repeating the operation and reset.
It is accordingly an object of the present invention to provide a starting device of a single phase induction motor for reducing power consumption. It is a further object to provide a starting device which restarts a single phase induction motor in a short time.